Cast booster assembly

ABSTRACT

The invention provides a booster assembly for a main explosive wherein the booster charge is formed from TNT and PETN and/or RDX and contains less RDX and/or PETN than required in comparably performing conventional booster charges of the cyclotol and pentolite types. The booster charge is a layer of a cast explosive of the group of pentolites, cyclotols and mixtures thereof, and a layer of cast TNT contiguous thereto. On a weight ratio basis, preferred pentolites contain PETN/TNT of from 60/40 to 40/60; and preferred cyclotols contain RDX/TNT of from 75/25 to 50/50, including Composition B which is a 60/40 RDX/TNT containing 1 percent of a microcrystalline wax.

Unite States Patent [72] Inventor PhllipG.Newman KenviLNJ. [21] AppLNo.786,667 22 Filed Dec.24,ll968 [54] CAST BOOSTER ASSEMBLY 14 Claims, 4Drawing Figs.

(56] References Cited UNITED STATES PATENTS 3,212,438 10/1965 Lawrence102/24 3,256,814 6/1966 Kruppenbach et a1 102/24 KIQIIW 3,371,606 3/1968Cook et al. 102/24 FOREIGN PATENTS 697,413 11/1964 Canada 102/24 PrimaryExaminerVer1in R. Pendegrass Attorney-William F. Smith ABSTRACT: Theinvention provides a booster assembly for a main explosive wherein thebooster charge is formed from TNT and PETN and/or RDX and contains lessRDX and/or PETN than required in comparably performing conventionalbooster charges of the cyclotol and pentolite types. The booster chargeis a layer of a cast explosive of the group of pentolites, cyclotols andmixtures thereof, and a layer of cast TNT contiguous thereto. On aweight ratio basis, preferred pentolites contain PETN/T NT of from 60/40to 40/60; and preferred cyclotols contain RDX/TNT of from 75/25 to50/50, including Composition B which is a 60/40 RDX/T NT containing 1percent of a microcrystalline wax.

PATENTED SEP14I97I 3.604.353

PHI LIP G. NEWMAN INVENTOR.

BY Shaw/M ATTOR N EY CAST BOOSTER ASSEMBLY This invention relates tobooster-type initiator assemblies for main explosive charges. In oneaspect this invention relates to booster assemblies above-describedwherein the booster charge comprises contiguous cast layers of TNT and amixture of TNT with PETN and/or RDX, to provide for improved economicsand safety in utilization of booster charges of the pentolite andcyclotol-types. In another aspect thin invention relates to boosterassemblies above described wherein the booster charge is a layer of saidTNT together with a layer of pentolite or a cyclotol-type explosive.Other aspects of the invention will be apparent in light of theaccompanying disclosure and the appended claims.

A complete explosive assembly ready for firing comprises a mainexplosive charge and means for initiating detonation of same. One suchcomplete assembly comprises a combination of a cap-insensitive charge asa main explosive charge, a booster unit containing a booster typeexplosive charge as a secondary initiator, and an electric blasting capor a detonating fuse as the primary initiator. The booster charge isdetonated in response to actuation of the primary initiator, and themain charge is detonated in response to detonation of the boostercharge, to provide the full explosive force of the assembly.Booster-type initiators for explosives generally comprise a closed shelland a booster type explosive charge therein together with means orsupport of a primary initiator, such as a blasting cap and/or adetonating fuse, in detonating relationship with the booster charge.Usually, a well extending into the booster charge, and/or one or moretunnels extending through the booster charge, or a combination of both,serves to support a blasting cap or detonating fuse or a combination ofthe two. Dependent upon the particular booster charge, a blasting capmay be sufficient as the primary initiator. However, the blasting capmay be utilizable with one or more strands of detonating fuse, or, oneor more strands of detonating fuse may be utilized independently of theuse of a blasting cap. In all events, such a booster assembly generallycontains a single well, and/or one or more tunnels depending upon theneed at hand. In some instances a small portion of supplementalexplosive or inner sensitizer" of sensitivity greater than that of thebooster charge is present as an insert in the booster charge indetonating relationship with the primary initiator and in turn with thebooster charge to facilitate detonation of the booster charge inresponse to initiation of the primary initiator.

Most often the booster charge is PETN or RDX cast in admixture with TNTto form a resulting two ingredient charge, the art referring to thePETN/T NT mixtures as pentolites, and to the RDX/T NT mixtures ascyclotols or, cyclotols containing RDX in a specific ratio to TNT (60/40) and additionally about 1 percent wax, are also referred to ascomposition B. Pentolite, cyclotol and Composition B-type boostercharges are well known in the art.

Both PETN and RDX involve reactants, and process steps, leading to highcosts in their manufacture and hence the use of those materials, asbooster charge ingredients, has been disadvantageous from an economicsstandpoint. Further, these materials are highly sensitive and it isaccordingly desirable, for safety reasons, that they be utilized in assmall proportions as are feasible.

This invention is concerned with booster assemblies in which the boostercharge contains TNT together with one or both of PETN and RDX, utilizingsmaller RDX and PETN proportions than those required in conventionalcyclotol and pentolite-type booster charges of comparable performance;and is safer to handle and is less costly than are the conventionalpentolite and cyclotol cast charges.

In accordance with the invention a booster assembly for a main explosiveis provided in which the booster charge comprises TNT together with RDXand/or PETN and contains less of the RDX and/or PETN than required incomparably performing booster charges of the cyclotol andpentolite-type;

said booster charge comprising a layer of cast explosive selected fromthe group consisting of pentolites, cyclotols, and mixtures thereof, anda layer of cast TNT contiguous thereto.

In preferred practice, the booster charge is formed from one layer ofTNT and one layer of pentolite or of cyclotol. When desired, both RDXand PETN are ingredients with TNT to constitute a layer of castcyclotol-pentolite mixture contiguous to the cast TNT. Also, when thetop layer is the pentolite and/or cyclotol, it can be covered to topped,when desired, with an additional layer of the less sensitive TNT forimproved safety in handling and storage; and that practice isparticularly advantageous when the pentolite and/or cyclotol layer to beso covered is relatively thin, inasmuch as the covering TNT layer thenalso imparts strength to the thin pentolite and/or cyclotol layer forincreased resistance to physical failure during handling and storage.

Generally, the booster charge has an overall weight (all layers) of fromabout 85 to about 2500 grams, with variation of size of each of the twolayers over a broad range. The thickness of the cast layer of pentoliteand/or cyclotol can be greater or less than that of the TNT layer, oftenvarying from a thickness of say one-eighth inch up to 3 inches or more.The weight ratio of the cast TNT layer to the pentolite and/or cyclotollayer is generally within the range of from about 0.221 to about 8:1,although any suitable ratio outside the range can be utilized. Althoughthe booster assembly of the invention can be of any suitable shape, thethickness of each layer is generally at least about 1 inch andpreferably within the range offrom 1% to 3 inches.

In preferred practice of the invention, the pentolite contains PETN in aweight ratio to TNT of from about 60/40 to 40/60; the cyclotol layercontains RDX in a weight ratio to TNT of from about /25 to 50/50 and ofcourse, Composition B, a cyclotol, is a 60/40 RDX/T NT containing lpercent of microcystalline wax. On the above bases, the amount of PETNor RDX in the booster assembly of the invention is generally from about10 to 50 percent of that which would be utilized in a conventional castpentolite or cyclotol booster charge of comparable sensitivity on, andinitiator strength. The invention is further illustrated with referenceto the drawings of which FIG. 1 shows a layered booster assembly of theinvention containing a cast pentolite layer superposed on, andcontiguous with, a cast TNT layer together with an insert extending intothe pentolite layer in conjunction with a single tunnel and a cap welleach as primary initiator support means; FIG. 2 shows an assembly, thesame as FIG. 1 except that it illustrates a double tunnel structure assupport means for the primary initiator, with the insert supportedentirely within the pentolite layer; FIG. 3 shows an assembly the sameas FIG. 1 except that it illustrates a single tunnel as support for theprimary initiator and an insert extending into the pentolite layer; andFIG. 4 is the same as FIG,. 3 except that it shows a cap well, assupport means for the primary initiator. It is to be understood thatalthough, in all figures, the drawings illustrate an insert, as anelement of the assembly, the structure is optional dependent upon theparticular initiation requirements. Similarly, whether support means forthe primary initiator is one or more tunnel member or a cap well, or anycombination of those elements, is a matter of choice to be made in lightof the particular initia tion requirements.

Referring to FIG. I, booster shell 10, closed at one end by closure 11and at the other end by closure 12 contains cast TNT layer 13 and castpentolite layer 14 superposed on layer 13 and contiguous thereto. Layer14 contains PETN in a weight ratio to TNT preferably in the order ofabout 0.6:! to 1521.

Well member 16, having closed end 17, extends into shell 10, closed end17 first, through end closure 12 with closed end 17 terminating withinpentolite layer 14; and with the opposite, and open end 17a supported inclosure 12 in open communication with the outside of shell 10, generallydisposed about flush, or nearly so, with the external wall of closure12. A tube member 18, open at both ends extends through closure 12,layers 13 and I4 and closure 11, to form a tunnel 18 extendingthroughout the booster assembly in open communication at each end withthe outside of shell 10. Conventional "insert" member 19 in shell is aclosed tube, containing additional explosive and extending from withinlayer 13 into layer 14 to be detonatable in response to action of aprimary initiator supported in well 16 or in tunnel l8 serverespectively to support an electric blasting cap, and detonating fuse,as primary initiator means for the layer charge 13-14; and are supportedso as always to be disposed, at least in part, in pentolite layer 14.Detonating relationship with layer 14. The "insert" explosive isadvantageously PETN which has greater sensitivity than that of eitherlayers 13 or 14; and it serves basically to facilitated detonation ofthe cast explosive 14 in response to initiation of the primaryinitiator.

In the fabrication of the assembly of FIG. 1 well member 16 and a tubemember for the formation of tunnel 18 are supported in closure 12 andemplaced in cylindrical shell 10 in position as shown except that endclosure 11 is not yet emplaced. Molten TNT, at about l80 F. is pouredinto shell 10 through the open end thereof to filI at least aboutone-half the shell. Insert 19 is then inserted into shell 10 through theopen end thereof and in the still molten TNT layer, preferably supportedin spaced position from the end closure 12, but in all events protrudingfrom within layer 13 into the top and unfilled portion of shell 10. TheTNT layer is then allowed to cool to about 190 F. and solidify andmolten pentolite at about 190 F. is then poured into shell 10 to formlayer 14 on top of, and contiguous with, layer 13. The molten pentolitelayer is then allowed to solidify by cooling. Closure member I1 isfastened in engaging relationship with tube 18, as support therefor,before or after solidification of the pentolite layer 14, as desired.

In FIGS. 2, 3 and 4 are shown embodiments of booster assembly of theinvention containing like parts of FIG. I which are, therefore, likenumbered. Parts of FIGS. 2, 3 and 4 corresponding to similar, but notidentical, parts of FIG. 1 are numbered by the same but primed numbers.Referring to FIG. 2, the assembly shown differs from that of FIG. 1 inrespect of primary initiator support means, and location of the insetmember. Thus, the assembly of FIG. 2 contains tunnels l8 andl8'extending through charge layers 13 and 14 and shell clonels forsupport of two separate strands of detonating fuse as the primaryinitiator for the layered charge. The insert I9, as shown, is optionallydisposed horizontally, and entirely. within the pentolite layer betweenthe two tunnel members.

Referring to FIG. 3 tunnel 18" extends through layers 13 and I4 andshell closures II and 12' as described with reference to tunnel 18 ofFIG. 1 to support a single strand of detonating fuse as the primaryinitiator for the layered charge. Optionally disposed insert 19', inshell 10, extends from within layer 13 into layer 14 as described withreference to insert 19 of FIG. I and is supported on the outer wall oftube 18" so as to be in direct detonating relationship with fuse typeprimary initiator means when supported in tunnel 18".

With reference to FIG. 4 well member 16' extends through shell closure12' and layer 13 into layer 14 terminating with closed end 17' withlayer 14 in direct contact therewith. Optionally disposed insert 19",within shell 10, extends from within layer 13 into layer 14 as describedwith reference to insert 19 of FIG. 1 and is supported on the wall ofwell l6in detonating relationship with a blasting cap when supported inwell 16 as a primary initiator for the layered charge. As stated withreference to the drawings, an insert member is optional dependent on theneed at hand. However, an insert is often advantageously utilized in thedetonation of the less sensitive of the layers 14 utilized such as apentolite layer 14 of PETN/TNT weight ratio of 40/60 or /55. Exemplaryof suitable insert members, are those in the order of from about 0.1 to3 grams, of PETN, RC8, and tetryl, although sizes outside that range canbe utilized when desired.

Any suitable primary initiator can be utilized in combination with abooster assembly of the invention, albeit it is always supported, atleast in part, within the cast layer 14 as illustrated with reference tothe drawings.

The invention is further illustrated with reference to the followingexamples.

A number of booster assemblies of FIG. 1 (except see foot note 2, Tablel) were fabricated, the insert consisting of 2.2: grams of PETN and thetwo layers 13 and 14 filling a closed paper tube 3 inches in length by 3inches in diameter. In all tests the layer 14 was pentolite having aPETN to TNT weight ratio of 45/55. In several series of tests, thevarious assemblies were detonated with either an electric blasting capor a detonating fuse and the force of the shots were measured in sures II and I2, 1n the same manner as described with 45 accordance with thestandard steel witness plate test. reference to tunnel 18 of FIG. I. toprovide a plurality of tun- The test are summarized as follows:

TABLE 1 Grams Primary initiator Diameter of hole cut TNT Pento- Primainwitness TNT: Pentolite, (layer lite 1 EB cap, cord. plate, Series weightratio 13) (layer 14) number grains inches About 1:1,

Test No.:

B About 1:1,

Test No.:

Test No.:

Series TABLE 1-( unlmucd Grams Primary initiator Diameter of hole cutPontollte (layer 14) EB cap,

TNT: l' 'entollte,

number weight ratio About 2.3:1,

Test No;

. About 4:1, Test No.:

Primacord, grains in witness plate, inches 1 PETN:TNT weight ratio was45/55.

1 In these tests, the insert, supported within the TNT layer 13, did notextend into layer 14 but did extend to the interface of the two layers13 and 14. Failures shown at Tests 2 and 4 (Primacord) and 3 and 4 (No.6 Cap) demonstrate need [or the insert to be disposed, at leastpartially, within the layer 13.

In another series of tests several booster assemblies of varyingproportions of cast layers, of FIG. 11, were fabricated, each includingthe same PETNzTNT weight ratio in the Pentolitc layer 14, and insertmember, the same as described with reference to the tests summarized inthe preceding table. Each booster was shot with a No. 8 electricblasting cap. Energy release data were determined in the mannerindicated by Cole (Cole, H. D., Underwater Explosions, PrincetonUniversity Press, Princeton, NJ. (1948), pages 228 to 285) and asreported by Sadwin (Sadwin, L. D., Cooley C. M., Porter, S. J., Stresau,R H., Underwater EvaIuation of the Performance of Explosives,International Symposium on Mining Research," Missouri, Feb. 1961,vol. 1) and his collaborators with some minor modifications. The resultsof the tests are summarized in the following tabulation;

Although the drawings and working examples are directed to reduction ofproportions of PETN in cast PETN-TNT-type type booster charges, theinvention is, of course, similarly applicable to the reduction of RDXproportions in the cast RDX- NTN booster compositions, in all instances,without significant loss in booster performance.

When referring herein to comparable performance of pentolite andcyclotol booster type charges of the prior art, it is ment particularlyto refer to energy and sensitivity characteristics. Thus a layeredcharge of a booster assembly of the invention provides for a markedreduction in proportions of RDX and/or PETN required to accomplishsubstantially the same energy and sensitivity characteristics of aconventional cyclotol or pentolite cast charge.

As will be evident to those skilled in the art, various modifi- TABLE 2Shock energy Bubble Shock Total Volume compared to Grams energy, energy,energy, energy, 100% Pento- Booster charge. TNTzPen- Test TNT Density,ft. Lbs/ it. Lbs./ it. Lbs./ ft. Lbs./ lite shock tolite (weight ratio)Number (layer 13) gins/cc. lb. 1() lb. 10 lb. l0 {tax10 energy About1:1. 1 240 1.53 804 690 1,494 1,426 .99 2 240 I, 53 760 677 1, 437 1,372 96 About 1. 5:1 1 286 1. 54 776 673 1, 449 1, 392 96 2 286 1.56 750641 1, 391 1, 354 .92

About 2. 3:1 1 336 1. 54 746 613 1, 359 l, 306 90 2 336 1. 54 766 575 1,341 l, 289 .89

About 4:1. 384 1. 59 751 569 1, 320 1, 309 .88 2 384 1. 59 747 514 1,261 1, 251 84 1 pound Pentolite l 1. 53 766 733 1, 499 1,431 l. 0

1 Cast Pentolite, PETNzTNT weight rati045/55,

cations can be made or followed, in the light of the foregoingdisclosure and discussion, without departing from the spirit or scope ofthe disclosure or from the scope of the claims.

What I claim and desire to protect by Letters Patent is:

1. In a booster assembly for a main explosive, wherein the v boostercharge is formed from TNT together with RDX and/or PETN, the improvementcomprising as said booster charge a layer of a cast explosive selectedfrom the group consisting of pentolites, cyclotols, and mixturesthereof, and a layer of cast TNT, each said layer having a transversesurface of substantially the same size and shape as of the other andcontiguous with the other only on an interface common to all of eachsaid surface, said booster charge thereby requiring less RDX and/or PETNthan required in conventional cyclotol and pentolite-type boostercharges of comparable performance.

2. in a booster assembly of claim 1. means for support ofa primaryinitiator for said booster charge within said layer of cast explosivecontiguous to said TNT.

3. A booster assembly of claim 2 wherein the thickness of said layercontiguous to said TNT if from about one-eighth to 3 inches and theweight ratio of said cast TNT to said layer of explosive contiguousthereto is within the range of from about 0.2:] to 8: l.

4. In a booster assembly of claim 3, said pentolite containing PETN in aweight ratio to TNT of from about 60/40 to 40/60, and said cyclotolcontaining RDX in a weight ratio to TNT of from about 75/25 to 50/50;and an insert member, within said charge, containing from 0.1 to 3 gramsof an explosive of the group of PETN, tetryl, and RDX and disposed. atleast in part within said layer of cast explosive contiguous to said TNTfor detonation in response to action of a primary initiator whensupported as described.

5. A booster assembly of claim 4, wherein said explosive contained insaid insert in PETN, and said layer of explosive contiguous with saidTNT is a pentolite.

6. A booster assembly of claim 5 wherein said pentolite contains PETN ina weight ratio to TNT of 45/55, and about 2.25 grams of said PETN iscontained in said insert member.

7 A booster assembly of claim 5 wherein said booster charge has anoverall weight in the range of from 85 to about 2500 grams. [9

8. A booster assembly of claim 7 wherein said layer of explosivecontiguous to said layer of cast TNT is a top layer of said boostercharge, and a cover layer of cast TNT superposed on said top layer.

9. In a booster assembly of claim 2 at least one tunnel member extendingthrough said booster charge for support of a detonating fuse as saidprimary initiator.

10. in a booster assembly of claim 2, an insert member containing anexplosive of the group of PETN, tetryl, and RDX; and disposed, at leastin part. with said layer of cast explosive contiguous to said TNT fordetonation in response to action of a primary initiator supported asdescribed.

11. In a booster assembly of claim 2 a well member extending into saidbooster charge and terminating within said layer of cast explosivecontiguous to said TNT for support of a blasting cap as said primaryinitiator.

12. in a booster assembly for a main explosive, wherein the boostercharge is formed from TNT together with RDX and/or PETN, the improvementcomprising as said booster charge a cylindrical layer of a castexplosive selected from the group consisting of pentolites, cyclotolsand mixtures thereof, and acylindrical layer of cast TNT; and saidcylindrical layers disposed contiguous with the other in abuttedend-to-end relationship, said booster charge thereby requiring less RDXand/or PETN than required in conventional cyclotol and pentolite typebooster charges of comparable performance.

13. In a booster assembly of claim 12, means for support of a primaryinitiator for said booster charge within said layer of cast explosivecontiguous to said TNT; said pentolite containing PETN in a weight ratioto TNT of from about 60/40 to 40/60 and said cyclotol containing RDX ina weight ratio to TNT of from about 75/25 to 50/50; and an insert memberwithin said charge, containing from 0.1 to 3 grams of an explosive ofthe group of PETN, tetryl and RDX and disposed, at least in part, withinsaid layer of cast explosive contiguous to said TNT for detonation inresponse to action of a primary initiator when supported as described.

14 A booster assembly of claim 13 wherein said explosive contained insaid insert member is PETN, and a cylindrical layer of cast pentolite insaid end-to-end relationship with said cylindrical layer of TNT.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,604,353 Dated September 14, 1971 Inventor(s) Phillip G. Newman (Case4) It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 9, "thin" should read -this- Column 1, line 27*, "or"should read for Column 2, line 1, "of cast" should read of a cast--Column 2, line 9, "to" should read -or- Column 2, line 25*, "the" shouldread -that- Column 2, line 54*, "drawings illustrate" should readdrawing illustrates-- Column 3, line 6, after "layer 14" insert anddisposed so as Column 3, line 7, after "18" insert (peri0d)- Colunm 3,line 7, after "18. insert Cap well 16 and tunnel l8-- Column 3, line 11,the sentence reading "Detonating relationship with layer 14. should bedeleted Column 3, line 27*, "190" should read --l72-- Column 4, line 6,ll should read ll"- Column 4, line 16, "with" should read within- Column4, line 28*, "RCS" should read R.DX

Column 5, table 1, line 5 of footnotes, "layer 13" should L read -layerl4- Patent No.

UNITED STATES PATENT OFFICE Dated Septe@er 14. 1971 Inventr(B)n (Case 4It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column Column C lumn Column Page 2 line 38, "and insert" should read andan insert-- line 39, "NTN" should read --TNT- line 43, "ment" shouldread meant line 12, Claim 3, "if" should read -is (second occurrence)line 27, "in" should read isline 33, Claim 7, after l9-- should bedeleted line 6, Claim 10, "with" should read within line 18, Claim 12,--a cylindrical-- "acylindrical" should read Signed and sealed this 21stday of March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,'JR. Attesting Officer ROBERT GOTTSCHALK Commissionerof Patents

2. In a booster assembly of claim 1, means for support of a primaryinitiator for said booster charge within said layer of cast explosivecontiguous to said TNT.
 3. A booster assembly of claim 2 wherein thethickness of said layer contiguous to said TNT if from about one-eighthto 3 inches and the weight ratio of said cast TNT to said layer ofexplosive contiguous thereto is within the range of from about 0.2:1 to8:
 4. In a booster assembly of claim 3, said pentolite containing PETNin a weight ratio to TNT of from about 60/40 to 40/60, and said cyclotolcontaining RDX in a weight ratio to TNT of from about 75/25 to 50/50;and an insert member, within said charge, containing from 0.1 to 3 gramsof an explosive of the group of PETN, tetryl, and RDX and disposed, atleast in part within said layer of cast explosive contiguous to said TNTfor detonation in response to action of a primary initiator whensupported as described.
 5. A booster assembly of claim 4, wherein saidexplosive contained in said insert in PETN, and said layer of explosivecontiguous with said TNT is a pentolite.
 6. A booster assembly of claim5 wherein said pentolite contains PETN in a weight ratio to TNT of45/55, and about 2.25 grams of said PETN is containeD in said insertmember.
 7. A booster assembly of claim 5 wherein said booster charge hasan overall weight in the range of from 85 to about 2500 grams. 19
 8. Abooster assembly of claim 7 wherein said layer of explosive contiguousto said layer of cast TNT is a top layer of said booster charge, and acover layer of cast TNT superposed on said top layer.
 9. In a boosterassembly of claim 2 at least one tunnel member extending through saidbooster charge for support of a detonating fuse as said primaryinitiator.
 10. In a booster assembly of claim 2, an insert membercontaining an explosive of the group of PETN, tetryl, and RDX; anddisposed, at least in part, with said layer of cast explosive contiguousto said TNT for detonation in response to action of a primary initiatorsupported as described.
 11. In a booster assembly of claim 2 a wellmember extending into said booster charge and terminating within saidlayer of cast explosive contiguous to said TNT for support of a blastingcap as said primary initiator.
 12. In a booster assembly for a mainexplosive, wherein the booster charge is formed from TNT together withRDX and/or PETN, the improvement comprising as said booster charge acylindrical layer of a cast explosive selected from the group consistingof pentolites, cyclotols and mixtures thereof, and acylindrical layer ofcast TNT; and said cylindrical layers disposed contiguous with the otherin abutted end-to-end relationship, said booster charge therebyrequiring less RDX and/or PETN than required in conventional cyclotoland pentolite type booster charges of comparable performance.
 13. In abooster assembly of claim 12, means for support of a primary initiatorfor said booster charge within said layer of cast explosive contiguousto said TNT; said pentolite containing PETN in a weight ratio to TNT offrom about 60/40 to 40/60 and said cyclotol containing RDX in a weightratio to TNT of from about 75/25 to 50/50; and an insert member withinsaid charge, containing from 0.1 to 3 grams of an explosive of the groupof PETN, tetryl and RDX and disposed, at least in part, within saidlayer of cast explosive contiguous to said TNT for detonation inresponse to action of a primary initiator when supported as described.14 A booster assembly of claim 13 wherein said explosive contained insaid insert member is PETN, and a cylindrical layer of cast pentolite insaid end-to-end relationship with said cylindrical layer of TNT.